This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A274689 #13 Jul 07 2016 02:23:54 %S A274689 1,-1,2,6,11,8,15,10,19,13,25,21,14,30,22,39,29,20,38,27,50,37,61,49, %T A274689 35,63,48,32,58,41,72,54,34,67,46,82,60,100,81,57,99,76,51,94,68,112, %U A274689 85,56,101,73,120,90,59,111,79,132,98,65,127,92,55,119,83,149 %N A274689 A variation of A005228. %C A274689 This is the lexicographically earliest sequence such that the absolute value of its first differences (A274690) is minimal, and together with its first differences, contains every integer except zero at most once. %C A274689 Each term is chosen so that |a(n+1) - a(n)| is minimal such that neither a(n+1) nor (a(n+1) - a(n)) has occurred previously in either this sequence or this sequence's first differences. If for a minimal term |k| k and -k are both available, choose the term that will minimize |a(n+1)|. %C A274689 It appears that this sequence together with its first differences list every integer except zero. %C A274689 Is -1 the only negative term? %e A274689 a(1) = 1; the next number with the lowest possible absolute value that has not occurred yet is -1, but since 1 + (-1) = 0 (which is not available because if a(n) = 0, then a(n+1) = a(n+1) - a(n)), -1 is not available. The next available terms are 2 and (-2). (-2) is chosen because |1 + 2| > |1 + (-2)|, so a(2) = 1 + (-2) = -1. %Y A274689 Cf. A005228, A274690. %K A274689 sign %O A274689 1,3 %A A274689 _Max Barrentine_, Jul 02 2016